Milestones for Roadmaps (Server)

As a Product Manager

I want to add Milestones to my Roadmap

So that I can visually communicate significant dates on my roadmap to stakeholders

Acceptance Criteria

1. User can create milestone(s) against a roadmap.
2. User can give the milestone a name and description(and specify a date)
3. Milestones should appear as lines on the chart (similar to the way current date works).
4. The user can drag the milestone to different dates.
5. The user should see the name of a milestone is on the roadmap view.
6. User can add and remove milestones from the view using the filters above the main chart.
7. A user can select a milestone to edit or delete it.